The invention relates to a magnetic head comprising at least two metal plates at least one of which comprises a ferromagnetic alloy, which are spot welded together along an interface.
Specific examples of such magnetic heads are magnetic heads with ferromagnetic lamellae assemblies, magnetic heads having a tape contact face consisting of a ferromagnetic plate or plates, magnetic heads with ferromagnetic lamellae welded on a base plate, and magnetic heads with butt welded magnetic core halves of ferromagnetic lamellae. In all these cases, there is a plate shaped ferromagnetic component which is pointwise spot welded to a second plate shaped component either also of ferromagnetic material or of another metal. A conventional contactless welding method may be used, such as electric arc welding, laser welding, electron beam welding, or plasma welding. These contactless welding methods are particularly suitable because they have the advantages that there is no mechanical load such as occurs in resistance welding upon applying the electrodes, that a large amount of energy can be supplied during a short time to produce a fusion weld without detrimental heating of the components, and also the danger of the components moving relative to each other is reduced.
A typical ferromagnetic alloy for use in magnetic heads comprises 4 to 12% by weight of Si, 3 to 18% by weight of Al, the balance being Fe together with the usual impurities. Various modifications to this alloy may be employed which comprise various additions: for example, up to 5% by weight of P (see German Offenlegungsschrift No. 2,944,790); up to 7% by weight of yttrium and/or rare earth metals (see U.S. Pat. No. 4,065,330); a quantity of B (see German Auslegeschrift No. 2,604,057); a quantity of Ti, Zr, Mn, Nb, Ta, Mo, Cr, V and/or W (see British Pat. No. 1,513,298); up to 3% by weight of Hf, Th, Sc, Cd and/or Mg (see U.S. Pat. No. 3,663,767).
When one of the components to be welded together comprises an Al-Fe-Si alloy, crack formation often occurs in the Al-Fe-Si component around the area of the welds. In Japanese Patent Application No. 52-9709, laid open to public inspection as Kokai No. 53-95847, said crack formation is ascribed to the formation of stresses as a result of the rapid cooling of the material after the welding operation; the solution proposed is to preheat the components to be welded together at a temperature between 300.degree. and 1400.degree. C., the exact preheating temperature depending on the particular Al-Fe-Si composition used and preferably being above 1000.degree. C. However, this method has not been proven to be entirely satisfactory because it is less suitable for mass production.